Lightweight high capacity combustion heater



LIGHTWEIGI-IT HIGH CAPACITY COMBUSTION HEATER 4 Sheets-Sheet 1 Filed Nov. 23. 1954 July 1, 1958 s. F. MULFoRD 2,841,135

l LIGHTWEIGHT HIGH CAPACITY COMBUSTION HEATER 4 Sheets-Sheet 2 Filed Nov. 25, 1954 wm s July 1, 1958 s. F. MuLFoRD 2,841,135

I..IGl-I'I'WEIGI1'1' HIGH CAPACITY COMBUSTION HEATER Filed Nov. 25. 1954 4 Sheets-Sheet 3 gg f /22/ yy .j ya' .f y/ ma 9 7 99 I will i 75 l 35 i 1"..

93 lmfmd July l, 1958 s. F. MULFORD 42,841,135

LIGHTWEIGHT HIGH CAPACITY COMBUSTION HEATER Filed NOV. 25, 1954 4 Sheets-Sheet 4 United States Patent LIGHTWEIGHT HGH CAPACITY CMBUSTION HEATER Stewart F. Mulford, Grinda, Calif., assigner to Stewart- Warner Corporation, Chicago, Ill., a corporation of Virginia Application November 23, 1954, Serial No. 470,655

The present invention relates to lightweight, high capacity combustion heaters suitable for use in aircraft for wing deicing and cabin heating purposes.

To minimize the size and weight of the heaters necessary for providing the large heat output required in this type of service, the heaters are operated at very high ternperatures. Moreover, the heaters are ordinarily cycled through periods of combustion at maximum capacity followed by standby periods in which little or no combustion takes place. Consequently the metal heat exchanging structure of heaters of this type is continually subject to rapid and extensive expansion and contraction by wide temperature changes which follow each other in rapid order. This tends to introduce troublesome stresses in the heaters shortening service life and limiting effective output capacity. The matter is further complicated by requirements of aircraft builders that the heat exchangers be capable of withstanding high internal pressures.

One object of the invention is to provide a high capacity aircraft type combustion heater which is largely free of damaging stresses even under the very severe temperature and pressure conditions attendant to intermittent operation in aircraft service.

Another object is to provide an improved heater of the character recited in the previous object which is considerably lighter in weight than conventional heaters of comparable heating capacity.

Other objects and advantages will become apparent from the following description of the form of the invention illustrated in the drawings, in which:

Figure 1 is an end View of combustion heater embodying the invention;

Fig. 2 is a longitudinal sectional View taken generally along the line 2-2 of Fig. 1;

Fig. 3 is a right end View of Fig. 2;

Fig. 4 is a fragmentary sectional View taken along the line 4--4 of Fig. 1;

Fig. 5 is a fragmentary sectional View taken along line 5-5 of Fig. 4;

Fig. 6 is a fragmentary sectional view taken along line 6-6 of Fig. 2;

Fig. 7 is a fragmentary sectional view taken along line 7--7 of Fig. l; and

Fig. 8 is a fragmentary sectional view taken along line 8 8 of Fig. 1.

As shown in Figs. l to 3, the combustion heater forming the illustrated embodiment of the invention comprises an elongated, generally cylindrical casing formed in two sections 22, 24 disposed in coaxial alignment with each other. The length of the right hand casing section 24, Fig. 2, is approximately three times that of the left hand casing section 22. Adjacent ends of thev two casing sections 22, 24 are spaced a short distance 26 from each other and yieldably coupled together by `an annular band 28 of rubber or similar flexible material. A metal channel and tension band 30 tightened around the exible band 28 holds the opposite marginal edges of the latter tightly against two outwardly convex beads 32 rolled in the adjacent marginal edges of the casing sections 22, 24.

A generally cylindrical metal shell 34 having substantially the same length as the casing 2t) is disposed concentrically within the casing. The shell 34 is considerably smaller in diameter than the casing Ztl and denes with the latter an annular space 36 of substantial radial thickness running the entire length of the casing. The air to be heated is circulated from left to right through the space 36, Fig. 2, from an annular air inlet opening 38 formed by the open left end of the casing 20 around the adjacent end of the shell 34 to an annular air outlet 40 formed by the open right end of the casing around the adjacent end of the shell.

The right end of the shell 34 is shaped as a truncated cone 42 having a length approximately one-fourth the overall length of the shell and a diameter at its small (right) end appraximately four-ifths that of the main portion of the shell.

The extreme right end of the shell 34 is closed by a circular header plate 44. An outwardly turned peripheral ilange 46 on the header 44 is seam welded at its extreme outer edge to the adjacent marginal edge of the shell 34.

The header 44 can be easily removed for inspection and repair of structure accessible from within the shell 34 merely by grinding oi the narrow welded edges of the header flange 46 and the shell section 42. 'The width of the tlange 46, which is turned at a right angle to the plane of the header 44, is substantially greater than that of the narrow weld, thus providing for re-welding of the header into place after it has been removed in the manner described.

A circulardivision member is mounted transversely in the central portion of the shell 34 by welding a peripheral ange 49 on the member to the inner surface of the shell. The division member 48 together with the end of the shell 34 to the right of the division member and the header 44 define a combustion chamber 50.

A central hole 52 formed in the division member 48 receives the open right hand end of a cylindrical element 54 of `a burner 55 coaxial with the shell 34. The opposite or left end of the burner element 54 is covered by a cap 56. A fuel nozzle and spark plug xture 58 of conventional construction is mounted on the outer end of the cap 56 and supported on three circumferentially spaced brackets 60 attached to the inner surface of the shell 34.

Combustion air enters'the burner 55 through a plurality of apertures 62 in the cylindrical wall of the burner element 54 and through an annular space 64 between a central hole 66 in the cap 56 and a burner nozzle 68 in the fixture 58.

The end of the shell 34 opposite the combustion chamber Sti is sealed by a removable cover '70 secured by bolts 72 to three circumferentially spaced brackets 74 attached to the adjacent marginal edge of the shell. The space within the shell 34 between the cover 7l? and the division member 48 forms a plenum chamber 76 around the burner 5S.

Air is supplied under pressure to the plenum chamber 76 through a cylindrical inlet conduit 73 which extends radially through the casing section 22 and enters the shell 34 in general alignment with the burner xture 58. Airtight seals 80, 82 are formed between the conduit 78 and the casing 20 and the shell 34, respectively. i

Air is supplied under pressure to the conduit 78 through a conduit 34 connected at right angles into the outer end of the conduit 78. ln aircraft use the conduit 34 is connected to suitable structure which supplies ram air under pressure. ln installations where ram air is not available a blower may 'oe used to provide the necessary air supply.

Fuel is supplied to the fixture 58 by a pipe 86 which 'extends out through the conduit 78 to a right angle connector 88 turned out -through the side portion of the conduit opposite the conduit 84. An electrical starting plug 90 in the burner fixture S8'is energized through an electrical cord 92 which extendsout through a central lseal 94 in a small header 96 closing the outer end of the conduit 78.

The ends of six fire tubes or conduits 98 are connected by sheet metal elbows 99 on the respective tubes into six circumferentially spaced circular openings b in the end of the tapered shell section 42 adjacent the header 44. The ends of the .elbows 99 extending into the openings 100 arevsomewhat enlarged and fit closely into inwardly turnedv edges 102 of the shell 3:4 encircling the respective holes. The edges 102 and the adjacent marginal end edges of the elbows y99 are welded together.

The opposite ends of the elbows 99 are butt welded to the adjacent ends of the tubes 98. From the juncture with its connecting elbow 99, each tube 9S forms a helix extendingaround the shell 34 in radially spaced relation to'both the shell and the casing 20 substantially to the mid-portion of the casing section 22.

The ends of the tubes 98 opposite the combustion chamber 50 are butt welded to sheet metal elbows 103 which connect with an exhaust manifold 104 mounted in the space 36 in general alignment along the axis of theshell 34 with the air inlet conduit 78.

As shown in Figs. l and 2, the manifold 104 is generally circular in shape as viewed along the axis of the casing and extends all the way around the shell 34 except for a relatively short circumferential break 106 which begins and ends on opposite sides of the combustion air inlet conduit 78. Rectangular in transversesection, as shown in Figs. 2, 7, and 8, the manifold 104 is fashioned from two radially spaced, cylindrical wall members 108, 110 welded to the inner and outer edges, respectively, of two radial end plates 112, 114. The radial width of the end plates 112, 114 is constant throughout the circumferential length of the manifold 104.

Opposite ends of the manifold 104 are closed by small plates 116 welded to the adjacent edges of the plates 108 to 114 (see Figs. l and 8). At the extreme ends of the manifold, the two cylindrical plates 10S, 110 have a width slightly less than that of the end plates 112, 114. From these extreme ends the cylindrical plates 10S, 110 are widened progressively toward the center of the manifold 104 located at the side of the shell 34 generally opposite from the air inlet conduit 78, Figs. l, 2 and 7.

The outlet ends of the elbows 103 on the lire tubes 98 are fastened into circumferentially spaced holes 118 in the adjacent manifold end plate 114, as shown in Fig. 4.

Exhaust gases collected in the manifold 11i-4 flow out through a generally cylindrical exhaust conduit 120 connected to the central portion of the outer cylindrical manifold member 103 and extending radially through the casing section 22 along the extended axis of the air inlet conduit 78.

A cylindrical radiation shield 122 encircles the central portion of the shell 34 betweenthe shell and the lire tubes 98 in radially spaced relation to both the shell and the tubes. Formed of sheet metal, the shield 122 is free of any direct connection to the shell 34.

Support for the shield 122 is provided by three sheet metal brackets 124 evenly spaced around the shield and extending radially between the shield and the casing 20 along the full length of the shield. As shown in Figs. l, 2 and 6, a right-angled flange 125 on the outer edge of each bracket 124 is fastened against the inner surface of the casing 20 by cap screws 126 extending through aligned holes in the casing 20 and the flange into threaded engagement with simplified sheet metal nut members 128 welded to the inner surface of the flange'. The aligned holes 130 in the casing 20 and the bracket ilange 125 which receive the screw 126 nearest 4the manifold 104 '4 are made substantially the same size as the screw to stabilize the bracket in relation to the casing. Similar aligned holes 132 in the ange and casing which receive the remaining screws 126 of the main bracket are made somewhat larger than the screws to allow shifting of the bracket in relation to the casing to avoid stresses due to temperature changes.

A series of spaced rectangular recesses 136 cut into each bracket 124 from the inner marginal edge of the bracket provide clearance for the fire tubes 98 extending around the shield 122. Flanged edges 138 of the brackets around the recesses provide loose support for the tubes 98. Flanges 140 on the interrupted inner edge of each bracket 124 are welded to the shield 122.

The heater thus provided has extraordinary freedom to expand and contract extensively without being subjected to damaging stresses. The inner shell 34 which contains the burner assembly and the combustion chamber 50 is directly connected only at one end to the outer casing 20. This connection is made through the air inlet conduit 78 with the shorter casing section 22. There is no direct connection between the inner shell structure and the longer casing section 24. The rather loose support provided for the lire tubes 98 from the casing section 24 affords some indirect support to the right end of the shell 34, Fig. 2, without restricting freedom of either the tire tubes or the shell to expand and contract in relation to the casing or to each other.

It will be appreciated further that the helical fire tubes 98 are inherently resilient in character and will yield freely without strain to compensate for any `differential expansion and contraction which may occur in the associated structure. Moreover, the shell structure 34 and the fire tubes 98 will expand and contract generally in the same direction along the axis of the burner, thus minimizing differential expansion and contraction of these parts.

Further assurance against the development of damaging stresses is provided by the flexible coupling structure 28 to 32 between the two casing sections 22, 24. Moreover, the exhaust manifold 104 is free of any direct connection with either the inner shell 34 or the outer casing section 24. Hence these elements are free to work relative to each other without stress.

Highly efficient operation of the heater is promoted by the counterflow of hot combustion gases through the fire tubes 98 in relation to the flow of Ventilating air from left to right, Fig. 2, through the air space 35. Moreover, the helical tubes 98 provide a Very large surface area for conducting heat to the passing Ventilating air stream in relation to the Volume of gases contained at any one time within the tubes.

The structurally simple radiation shield 122 serves to increase substantially the efficiency with which heat is transmitted from the structure of the combustion chamber 50 to the passing Ventilating air. It will be appreciated that the shell 34, when heated to a high temperature by combustion within the chamber 50, transmits yheat at a high rate directly to the Ventilating air by conduction from the exterior surface of the shell. The hot shell 34 also emits radiant heat at a high rate. By its nature this radiant heat tends to pass through the surrounding Ventilating air without heating the air substantially. However, the shield 122 positioned along the hottest portion of the shell 34 collects this radiant heat thus preventing it from unnecessarily and wastefully heating the fire tubes 98 and the surrounding outer casing 2t). The rw diant heat collected by the shield 122 is transmitted over the large interior and exterior :surfaces of the shield to the passing stream of Ventilating air to produce additional direct heating of the air. Consequently, a substantial gain in heating emciency is realized and the temperature of the outer casing 20 is kept relatively low.

The large heat transfer area provided by the fire tubes 93 permitsvv a minimization of the size of the combustion chamber without loss in heating etliciency. The relatively small `size of the combustion chamber Sil together with the inherent capacity of the tubes 98 to contain high internal pressures, eases the problem of meeting the requirement for aircraft use that the heater be capable of containing large internal pressure, While at the same time minimizing the overall weight of the heater.

While I have shown and described a preferred embodiment of my invention, it will be apparent that variations and modifications thereof may be made without departing from the principles and scope of the invention. l therefore desire, by the following claims, to include all such variations and modifications by which substantially the results of my invention may be obtained through the use of substantially the same or equivalent means.

l claim:

1. In a high capacity combustion heater, the combination of generally cylindrical casing means formed in first and second axial sections and defining at opposite ends thereof an inlet and an outlet for passing therethrough air to be heated, adjoining circumferential portions of said casing sections being spaced apart, resilient means bridging said adjoining portions of said casing sections circumferentially to connect said sections together yieldably for movement one relative to the other, combustion chamber means defining a combustion chamber ldisposed within said casing means in radially spaced relation thereto, means supporting one end of said combustion chamber means on said first casing section, said combustion charnber means being freely movable relative to said second casing section, a burner mounted to supply combustible gases to the end of said combustion chamber adjacent said first casing section, a multiplicity of flexible re tubes each having a helical shape, said respective re tubes having one end thereof connected to the end of said combustion chamber opposite the burner end thereof and extending through the casing means around and along said combustion chamber in radially spaced relation thereto to the burner end thereof, a common exhaust manifold mounted in said first casing section and connected to the adjacent ends of all of said fire tubes, -a generally cylindrical radiation shield encircling said combustion chamber means in radially spaced relation thereto and extending therealong between the combustion chamber means and said helical lire tubes, a plurality of supports attached to said second casing section in circumferentially spaced relation therearound and extending radially inward into supporting relation to said radiation shield, and said supports having portions thereof loosely engaging adjacent portions of said helical lire tubes to loosely support the latter and provide support therethrough to the end of said combustion chamber means attached thereto.

2. In a high capacity combustion heater, the combination of a casing, said casing defining at opposite ends thereof an inlet and an outlet for passing therethrough air to be heated, means defining a generally cylindrical combustion chamber disposed within said casing in radially spaced relation thereto, a burner mounted to discharge combustible gases into one end of said combustion chamber, said combustion chamber having an end portion opposite said burner end thereof formed radially inward to a reduced size diametrically, a multiplicity of elbows circumferentially spaced around said reduced end portion of the combustion chamber, said respective elbows having one end connected radially into said reduced end portion of the combustion chamber and spiraling outwardly therefrom, a multiplicity of helically shaped lire tubes connected at one end of saidrrespective elbows and extending through said casing around and along said combustion chamber in radially spaced relation thereto to the burner end thereof, a common exhaust manifold disposed at the burner end of said combustion chamber and connected to the adjacent ends of all of said `hre tubes, a cylindrical radiation shield encircling said combustion chamber in radially spaced relation thereto and extending therealong between said combustion chamber means and said helical tire tubes, a plurality of supports attached to said casing in circumferentially spaced relation thereto and extending radially inward into supporting relation to said radiation shield, and said supports having portions thereof loosely engaging said helical re tubes in loose supporting relation thereto.

3. In a high capacity combustion heater, the combination of generally cylindrical casing means defining `at opposite ends thereof an inlet and an outlet for passing therethrough air to be heated, elongated combustion chamber means defining a combustion chamber therein and disposed concentrically within said casing means in radially spaced relation thereto, means supporting one end of said combustion chamber means on the adjacent end of said casing means, the end of said combustion chamber means opposite said supported end thereof being freely movable relative to the adjacent end of said casing means, a burner mounted at the supported end of said combustion chamber means to supply combustible gases into the adjacent end of said combustion chamber, a multiplicity of helical lire tubes, said respective lire tubes each having one end thereof connected to said combustion chamber through the end of said combustion chamber means opposite said supported end thereof `and extending through said casing means around and along said combustion chamber means to the supported end of the latter in radially spaced relation to both said combustion chamber means and said casing means, an lexhaust manifold of arcuate shape mounted in said casing means and extending thereinto into spaced embracing relation to the supported end of said combustion chamber means, said manifold extending around the major portion of the circumference of said combustion chamber means and terminating circumferentially at two circumferential extremities spaced apart circumferentially with respect to said combustion chamber supporting means, said manifold being connected to the adjacent ends of all of said fire tubes, a generally cylindrical radiation shield encircling said combustion chamber means in radially spaced relation thereto and extending longitudinally therealong between the combustion chamber means and said helical lire tubes, a plurality of support brackets attached to the portion of said casing means encircling said radiation shield, said brackets being circumferentially spaced around said radiation shield and extendin(7 radially inward into supporting relation to the latter, and said brackets having portions thereof loosely engaging adjacent portions of said helical fire tubes to loosely support the latter.

References Cited in the le of this patent UNITED STATES PATENTS 9,969 Gore Aug. 30, 1853 1,674,213 McDowell June 19, 1928 1,712,260 Dybvig May 7, 1929 2,096,821 Noble Oct. 26, 1937 2,363,742 Norton Nov. 28, 1944 2,383,431 Weyenberg Aug. 21, 1945 2,447,373 vSmoot Aug. 17, 1948 2,531,939 Jacobs Nov. 28, 1950 

